mdai,

cychrou2

2-caneord wandde i

evices,for praized LIBty andof theuctivityolytes h

electr

dure. Their structures were conrmed by H- and C-NMR and

trolyte lm was men-nous solution was pre-X (0.25 g, 1.45 mmol),

Solid State Ionics 262 (2014) 761764

Contents lists available at ScienceDirect

Solid Stat

.ematrix for gel electrolytes have been reported as far as we know [14].In this paper we report preparation of poly(oxetane)-based gel

electrolytes from photo-initiated polymerization of oxetane derivatives

DDOE (0.22 g, 0.75 mmol), photo initiator [15,16] (diphenyliodoniumhexauorophosphate, DPIHFP, 0.04 g, 0.08 mmol) and PC (0.18 mL,2.10 mmol) at room temperature in the dark. The PC solutionwas pouredfour-membered cyclic ether. The polymer with TMO main chain haslower glass transition temperature. Some investigations of solid poly-mer electrolytes based on poly(oxetane) matrixes have been reportedwith their applications [513]. Few applications of poly(oxetane) as a

Detailed preparation procedure of a gel electioned in our previous paper [14]. The PC homogepared by mixing LiBF4 (0.04 g, 0.42 mmol), CMOpoly(ethylene oxide) (PEO), poly(methyl methacrylate) (PMMA),poly(acrylonitrile) (PAN) and poly(vinylidene uoride) (PVDF) [14].

Poly(oxetane)s which have trimethylene oxide (TMO) as their mainchain are prepared through ring-opening polymerization of oxetane, a

FTIR techniques.

2.2. Preparation of gel lms(CMOX, Fig. 1(a)) and cross-linker (DDOE or

Corresponding author. Tel.: +81 836 85 9282; fax: +E-mail address: tsutsumi@yamaguchi-u.ac.jp (H. Tsuts

0167-2738/$ see front matter 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.ssi.2013.09.049olytes in polymermatrix,ypically investigated bythe gel electrolytes are

grade and used as received. Monomer (CMOX) [9,10] and cross-linker (DDOE, TDOE) [57] were prepared by the literature proce-

1 13a normally cross-linked matrix, have been tmany scientists [14]. Matrix polymers for1. Introduction

Large-sized high energy storage dondary batteries (LIBs) are key devicesand wind power sources. The large-shigh energy storage but also high safepolymer electrolytes to the LIBs is oneand durability themselves. Lower condpolymer electrolytes than liquid electrmercial application to the LIBs.

Gel electrolytes which contain liquidsuch as lithium ion sec-ctical application of solars should offer not onlydurability. Application ofsolutions for high safetyat room temperature ofas prevented their com-

of a lithium electrode and plating and stripping processes of lithium in it.

2. Experimental

2.1. Chemicals

All reagents were used as received unless otherwise described.Propylene carbonate (PC) and lithium salts, LiBF4 and lithiumbis(triuoromethanesulfonyl)amide (LiTFSA) were lithium batterytheir performance as a gel electrolyte, conductivity, polarization behaviorCross-linked poly(oxetane) matrix for polylithium ions

Hiromori Tsutsumi , Asami SuzukiApplied Molecular Science, Graduate School of Medicine, Yamaguchi University, 2-16-1 Tokiwa

a b s t r a c ta r t i c l e i n f o

Article history:Received 17 May 2013Received in revised form 7 September 2013Accepted 9 September 2013Available online 12 October 2013

Keywords:Polymer electrolyteGel electrolyteCross-linked matrixPoly(oxetane)Lithium battery

Oxetane, four-membered(TMO, \CH2CH2CH2O\) tethylene oxide (EO, \CH2CHfrom copolymerization of 3-(chain and two terminal oxetor TDOE, lithium salt (LiBF4photo-initiator was irradiateprepared from CMOX, TDOEof lithium on a nickel electro

j ourna l homepage: wwwTDOE, Fig. 1(b), (c)) and

81 836 85 9201.umi).

ghts reserved.er electrolyte containing

Ube 755-8611, Japan

lic ether provides polymer compounds which have trimethylene oxidegh its ring-opening polymerization. New gel electrolyte lms with TMO andO\) chains were prepared. The cross-linked polymer matrixes were preparedyanethoxymethyl)-3-ethyloxetane (CMOX) and cross-linker which has oligo-EOrings coupled with the EO chain (DDOE or TDOE). The mixture of CMOX, DDOElithium bis(triuoromethanesulfonyl)amide, LiTFSA), propylene carbonate andith a high pressure mercury lamp. The maximum conductivity in the gel lmsLiBF4 was 1.52 mS cm1 at 353 K. Repeatable plating and stripping processes

n the gel electrolyte were conrmed by cyclic voltammetry measurement. 2013 Elsevier B.V. All rights reserved.

e Ionics

l sev ie r .com/ locate /ss iinto an aluminum foil dish and irradiated with a high-pressure mercurylamp (Optical Module X, USHIO, 7.5 J cm2) for 60 min at room temper-ature. The resulted lm presents as D(c-PCMOX)(LiBF4)20. This meansthat the D(c-PCMOX)(LiBF4)20 contains LiBF4 (0.42 mmol, 20% of molaramount of PC (2.1 mmol)). The molar ratio of CMOX to cross-linker(DDOE or TDOE) was xed at 29 to 15 in this investigation.

762 H. Tsutsumi, A. Suzuki / Solid State Ionics 262 (2014) 761764Fig. 1. Structures of (a)monomer (CMOX), (b), (c) cross-linkers (DDOE andTDOE) and (d)2.3. Measurements

An electrolyte lm was sandwiched with two stainless steel plates(13 mm in diameter). Conductivity of the electrolyte lmwasmeasuredwith an LCR meter (HIOKI 3532-80 chemical impedance meter,100 mVp p, 10100 kHz) under prescribed temperature conditionsfrom 293 K to 353 K. XRD patterns of the composite lmswere recordedwith an X-ray diffraction meter (Ultima IV (Protectus), Rigaku, CuK, = 0.1542 nm). Infrared spectra of samples were recorded with anFTIR spectrophotometer (IRPresatge-21, Shimadzu). 1H- and 13C-NMRspectra of the oxetane monomer, cross-linker, and resulted polymerswere obtained on anNMR spectrophotometer (JNM-Lambda-500, JEOL).

Electrochemical characterization of the solid polymer electrolytelms was performedwith polarization measurements of a lithium elec-trode and cyclic voltammetry measurements of a nickel electrode inpoly(oxetane)-based gel electrolyte lms. Detailed cell congurationsand procedures for these electrochemical measurements were reportedin our previous papers [17]. Electrochemical measurements wereperformed with a computer-controlled potentiogalvanostat (HZ-5000,Hokuto Denko) under Ar atmosphere (dew point was at 203 K) at333 K.

3. Results and discussion

The electrolyte lms prepared from CMOX and cross-linker (DDOEor TDOE) were transparent and exible. Their typical appearances areshown in Fig. 2. XRD measurements of the electrolyte lms wereperformed. The XRD results suggest that the added lithium salt intothe matrix is fully dissolved into the gel lms.

Temperature dependence of conductivity for the lithium-ion free gellms and the gel electrolyte lms with lithium salt prepared fromCMOX and cross-linker (DDOE or TDOE) is shown in Fig. 3. Conductivity

cross-linked poly(oxetane).

Fig. 2. Appearances of D(c-PCMOX)(LiX)30 lms, (a) X = BF4 and (b) X = TFSA.

Fig. 3. Temperature dependence of conductivity for the lithium salt-free D(c-PCMOX) andT(c-PCMOX)lms and the electrolytelmsD(c-PCMOX)(LiX)30 andT(c-PCMOX)(LiX)30,X = BF4 or TFSA.

Fig. 4. VTF plots of cross-linked poly(oxetane)-based gel electrolyte lms, D(c-PCMOX)(LiLiBF4)30 and T(c-PCMOX)(LiLiBF4)30.

763H. Tsutsumi, A. Suzuki / Solid State Ionics 262 (2014) 761764Table 1The number of charge carriers and apparent activation energy of ion transport estimatedfrom VTF equation.

Gel lm X n A/S K1/2 cm1 B/kJ mol1

D(c-PCMOX)(LiX)n BF4 20 0.0735 5.8030 1.07 6.14

TFSA 20 0.188 7.03at 303 K for the lithium-ion free gel lms, D(c-PCMOX) and T(c-PCMOX) lms was 17.2 S cm1 and 4.9 S cm1. This is due tosome amount of residual ions (PF6 and Ar2I+, Ar = benzene ring)which were produced with photolysis of photo-initiator, DPIHFP[15,16]. Conductivity of the D(c-PCMOX)(LiBF4)30 electrolyte was0.476 mS cm1 at 303 K, 1.45 mS cm1 at 353 K. Conductivity of the

30 1.94 7.4840 1.58 7.74

T(c-PCMOX)(LiX)n BF4 20 0.944 7.3530 5.63 8.19

TFSA 20 0.454 6.6330 9.03 8.8635 4.52 9.39

Fig. 5. Polarization curves of lithium electrode in the electrolyte lms, T(c-PCMOX)(LiX)30, X = BF4 and TFSA.T(c-PCMOX)(LiBF4)30 electrolyte was 0.254 mS cm1 at 303 K and1.52 mS cm1 at 353 K. As shown in Fig. 3, the temperature depen-dence curves of D or T(c-PCMOX) electrolyte lms are slightly convex.The curves are best tted to an expression of the Eq. (1):

AT1=2expB=R TT0 1

where is conductivity, is pre-exponential factor, which is propor-tional to the number of charge carriers, B is estimated activation energyfor conduction, R is gas constant, T is absolute temperature, and T0 isnormally called the equilibrium glass-transition temperature [18,19].

Fig. 4 shows typical VTF plots for the electrolyte lms, D(c-PCMOX)(LiBF4)30 and T(c-PCMOX)(LiBF4)30. The plots show the linearrelationships. The VTF plots of other poly(oxetane)-based gel electro-lyte lms prepared in our investigation also show the linear relation-ships. This indicates that viscoelastic character in the cross-linkedpoly(oxetane)-based gel lms affects migration of the ions [18,19].The estimated parameters, A and B are listed in Table 1. The estimatedactivation energy values (B in Table 1) of the gel electrolytes are in the

Fig. 6.Cyclic voltammogramof a nickel electrode in T(c-PCMOX)(LiBF4)30 electrolyte lmat 60 C, scan rate at 1 mV s1, (a) 1st cycle and (b) from 2nd cycle to 5th cycle.

range 5.80 kJ mol1 to 9.39 kJ mol1. The values are almost equal to orlower than those of the gel electrolyte systems, PMMA-based gel electro-lytes (3.33 kJ mol1 to 9.72 kJ mol1) [20], and PAN-based gel electro-lytes (10.6 kJ mol1 to 14.0 kJ mol1) [21].

Electrochemical deposition and dissolution of lithium in a gel electro-lyte system are key processes for application of the electrolyte to lithiummetal secondary batteries. Electrochemical responses of lithium ions inthe gel electrolytes were checked by two-type measurement, polariza-tion measurement technique of a lithium electrode and potentialsweep of a nickel electrode in the gel electrolytes to check on the platingand stripping processes of lithium.

Fig. 5 shows the polarization curves of a lithium electrode in the T(c-PCMOX)(LiX)30 (X = BF4 or TFSA) electrolyte at 333 K. The polariza-tion curves of lithium electrode in the gel lm gave asymmetricalforms, which is fairly different from those observed in liquid electro-lytes. Decrease in concentration of lithium ions at the lithium/gel inter-face under the highly cathodic polarized condition may be induced bythis phenomenon. It also suggests that the transportation rate of lithiumions from the electrolyte bulk to the interface between an electrode andan electrolyte lm is slower than that in liquid electrolytes.

Fig. 6 shows the cyclic voltammogram at the 1st cycle (a) and fromthe 2nd to 5th cycles (b) of a nickel electrode in the T(c-PCMOX)(LiBF4)30 electrolyte. In cathodic potential scan from ca. 3 V to1 V increasein cathodic current is attributed to the lithiumdeposition process on thenickel electrode in the gel electrolyte. Anodic peak at 0.1 Vwhich is dueto dissolution of the plated lithium from the nickel plate is also ob-served. As shown in Fig. 6(b), plating and stripping processes of lithiumon the nickel electrode are repeatable in the electrolyte lm. This obser-

can be used for rechargeable lithium metal secondary batteries.

has oligo-ethylene oxide units. The resulted gel electrolyte lms weretransparent, exible, and amorphous. The maximum conductivity was1.52 mS cm1 at 353 K in the T(c-PCMOX)(LiBF4)30 gel lm. Repeat-able plating and stripping processes of lithium on a nickel electrode inthe gel electrolyte were conrmed by cyclic voltammetry measurement.The poly(oxetane)-based gel electrolyte lms are one of the candidatesas a polymer electrolyte of lithium metal secondary batteries.

Acknowledgments

This work was partially nancial supported by the Grant-in-Aid forScientic Research (C), KAKENHI (21560883) and the Electric Technol-ogy Research Foundation of Chugoku.

References

[1] J.Y. Song, Y.Y. Wang, C.C. Wan, J. Power. Sources 77 (2) (1999) 183.[2] A. Manuel Stephan, K.S. Nahm, Polymer 47 (16) (2006) 5952.[3] B. Scrosati, Chem. Rec. 5 (5) (2005) 286.[4] A.M. Stephan, Eur. Polym. J. 42 (1) (2006) 21.[5] Y. Miwa, H. Tsutsumi, T. Oishi, Polym. J. 33 (12) (2001) 927.[6] Y. Miwa, H. Tsutsumi, T. Oishi, Polym. J. 33 (8) (2001) 568.[7] Y. Miwa, H. Tsutsumi, T. Oishi, Electrochemistry 70 (4) (2002) 264.[8] R. Shibutani, H. Tsutsumi, J. Power. Sources 202 (2012) 369.[9] Y. Shintani, H. Tsutsumi, J. Power. Sources 195 (9) (2010) 2863.

[10] Y. Shintani, H. Tsutsumi, Electrochemistry 78 (5) (2010) 387.[11] L. Ye, Z.G. Feng, Y.F. Su, F. Wu, S. Chen, G.Q. Wang, Polym. Int. 54 (10) (2005)

1440.[12] L. Ye, P. Gao, F. Wu, Y. Bai, Z.g. Feng, Polymer 48 (6) (2007) 1550.[13] J.B. Kerr, G. Liu, L.A. Curtiss, P.C. Redfern, Electrochim. Acta 48 (2003) 2305.[14] A. Suzuki, H. Tsutsumi, Jpn. J. Polym Sci. Technol. 70 (1) (2013) 10.[15] J.V. Crivello, J.L. Lee, J. Polym. Sci. A Polym. Chem. 27 (12) (1989) 3951.[16] J.V. Crivello, B. Falk, M.R. Zonca Jr., J. Polym. Sci. A Polym. Chem. 42 (7) (2004) 1630.

764 H. Tsutsumi, A. Suzuki / Solid State Ionics 262 (2014) 7617644. Conclusion

Weprepared poly(oxetane)-based gel electrolyte lms from oxetanederivative with cyanoethoxymethyl side chain and cross-linker which[17] H. Tsutsumi, M. Yamamoto, M. Morita, Y. Matsuda, T. Nakamura, H. Asai, J. Power.Sources 41 (3) (1993) 291.

[18] P.G. Bruce, F.M. Gray, in: P.G. Bruce (Ed.), Solid State ElectrochemistryCambridgeuniversity press, 1995, pp. 119162.

[19] M.A. Ratner, P. Johansson, D.F. Shriver, MRS Bull. 25 (3) (2000) 31.[20] O. Bohnke, G. Frand, M. Rezrazi, C. Rousselot, C. Truche, Solid State Ionics 66 (1993)

97.[21] U.-S. Park, Y.-J. Hong, S.M. Oh, Electrochim. Acta 41 (6) (1996) 849.vation supports the nding that the T(c-PCMOX)(LiBF4)30 electrolyte

Cross-linked poly(oxetane) matrix for polymer electrolyte containing lithium ions1. Introduction2. Experimental2.1. Chemicals2.2. Preparation of gel films2.3. Measurements

3. Results and discussion4. ConclusionAcknowledgmentsReferences